There are many industries in which it is necessary to produce relatively complex components having good mechanical properties but that are relatively cheap, produce little waste material and have a low scrap rate in production. Such components may be components for a gas turbine engine, such as an integrally bladed disc (known as a blisk) for a compressor or turbine stage.
Typically, such components are machined from wrought material. Whilst machining from a wrought material block provides a component with good mechanical properties, it can result in large amounts of material being machined away as waste. Furthermore, to produce complex shapes, particularly having tight tolerances, may require considerable machining time and/or complex tooling to achieve the desired profiles.
An alternative conventional method of producing such articles or components is by casting, which produces less waste material than machining from wrought. Complex components may require additional protrusions to assist in supporting the component and controlling material distribution during the casting process. Therefore, cast components may require subsequent machining to remove these additional protrusions. Nevertheless, there is less material wastage, and hence expense, in casting complex components than in machining from wrought. However, one problem with this method is that casting is a relatively lengthy process since a sacrificial mould must be formed, the molten material poured into the mould, the mould and molten material slowly cooled and then the mould removed.
Another problem with casting is that the mechanical properties of a cast component are relatively poor due to porosity caused by entrapped gases and shrinkage, inhomogeneous structure, inclusions and segregation within the component. The component is also prone to significant shrinkage due to the large thermal expansion coefficient during the liquid to solid phase change. In most cases, this leads to a requirement for the casting to be larger than the desired end component size. The poor mechanical properties may make castings unsuitable for some applications, especially those in fatigue situations, or lead to a high scrap rate in production due to the high product integrity required.
A still further conventional method of joining components is by electron beam welding as shown in U.S. Pat. No. 5,390,413. Although this is an effective joining method, a problem with it is the microstructural changes and phase changes caused in and around the weld area by the heat effects. This can weaken the bond between component parts, stress the component parts and/or change the properties of the resultant article. Other problems are the relatively large amount of post-weld machining required to achieve the desired shape, the component design limitations imposed by the heavy tooling and required welding motion, and the high levels of capital investment and development work required to produce new components.
The present invention seeks to provide a method of manufacturing an article by joining component parts, and an article formed thereby, that seeks to address the aforementioned problems.